Microfluidic system

ABSTRACT

The present invention relates to a method for presenting an analyte of a liquid sample as an MS-analyte to a mass spectrometer. More particularly, the method comprises the steps of applying a liquid sample containing the analyte to a sample inlet port of a microchannel structure of a microfluidic device, said structure also comprising an outlet port (MS-port) that is capable of being interfaced with a mass spectrometer, passing the analyte to the MS-port thereby transforming it to an MS-analyte, and presenting the MS-analyte to mass spectrometer via the MS-port.

This application is a continuation of U.S. application Ser. No.10/621,868 filed Jul. 17, 2003 issued as U.S. Pat. No. 6,812,457, whichis a continuation of U.S. application Ser. No. 09/811,741 filed Mar. 19,2001 issued as U.S. Pat. No. 6,653,625.

TECHNICAL FIELD

The present invention relates to a microfluidic device, which can beinterfaced to a mass spectrometer (MS). The device comprises amicrochannel structure having a first port (inlet port) and a secondport (outlet port). A sample to be analysed is applied to the first portand presented to the mass spectrometer in the second port. This secondport will be called an MS-port. There may be additional inlet and outletports. During passage through the microchannel structure the sample isprepared to make it suitable for analysis by mass spectrometry.

The sample presented in an MS-port will be called an MS-sample. Ananalyte in an MS-sample is an MS-analyte. “Sample” and “analyte” withoutprefix will primarily refer to a sample applied to an inlet port.

One important aspect of the present invention concerns mass spectrometryin which the MS-samples are subjected to Energy Desorption/Ionisationfrom a surface by input of energy. Generically this kind of process willbe called EDI and the surface an EDI surface in the context of theinvention. Typicallly EDIs are thermal desorption/ionisation (TDI),plasma desorption/ionisation (PDI) and various kinds of irradiationdesorption/ionisation (IDI) such as by fast atom bombardment (FAB),electron impact etc. In the case a laser is used the principle is calledlaser desorption/ionisation (LDI). Desorption may be assisted bypresenting the MS analyte together with various helper substances orfunctional groups on the surface. Common names are matrix assisted laserdesorption/ionisation (MALDI) including surface-enhanced laserdesorption/ionisation (SELDI). For MALDI see the publications discussedunder Background Publications below. For SELDI see WO 0067293 (CiphergenBiosystems).

The surface from which desorption/ionisation is intended to take placeis called an EDI surface.

By microformat is meant that in least a part of the microchannelstructures the depth and/or width is in the microformat range, i.e. <10³μm, preferably <10² μm. In the most typical microformat structureseither the width and/or the depth are in principle within these rangesessentially everywhere between the sample inlet port and the MS-port.

BACKGROUND PUBLICATIONS

For some time there has been a demand for microfluidic sample handlingand preparation devices with integrated MS-ports. This kind of deviceswould facilitate automation and parallel experiments, reduce loss ofanalyte, increase reproducility and speed etc.

-   -   WO 9704297 (Karger et al) describes a microfluidic device that        has an outlet port that is claimed useful when conducting        electrospray ionisation mass spectrometry (ESI MS), atmospheric        pressure chemical ionisation mass spectrometry (APCI MS), matrix        assisted laser desorption/ionisation mass spectrometry (MALDI        MS) and a number of other analytical principles.    -   U.S. Pat. No. 6,110,343 (Ramsey et al) describes an electrospray        interface between a microfluidic device and a mass spectrometer.    -   U.S. Pat. No. 5,969,353 (Hsieh) describes an improved interface        for electrospray ionization mass spectrometry. The interface is        in the form of an electrospray tip connected to a microchannel        structure of a chip.    -   U.S. Pat. No. 5,197,185 (Yeung et al) describes a laser-induced        vaporisation and ionization interface for directly coupling a        microscale liquid based separation process to a mass        spectrometer. A light-adsorbing component may be included in the        eluting liquid in order to facilitate vaporisation.    -   U.S. Pat. No. 5,705,813 (Apffel et al) and U.S. Pat. No.        5,716,825 (Hancock et al) describe a microfluidic chip        containing an interface between a microfluidic device and an        MALDI-TOF MS apparatus. The microfluidic device comprises    -   (a) an open ionisation surface that may be used as the probe        surface in the vaccum gate of an MALDI-TOF MS apparatus (column        6, lines 53–58 of U.S. Pat. No. 5,705,813) or    -   (b) a pure capture/reaction surface from which the MS-analyte        can be transferred to a proper probe surface for MALDI-TOF MS        (column 12, lines 13–34, of U.S. Pat. No. 5,716,825).

These publications suggest that means, such as electrical connections,pumps etc, for transporting the liquid within a microchannel structureof the device are integrated with or connected to the device. This kindof transporting means imposes an extra complexity on the design and use,which in turn may negatively influence the production costs, easiness ofhandling etc of these devices.

U.S. Pat. No. 5,705,813 (Apffel et al) and U.S. Pat. No. 5,716,825(Hancock et al) are scarce about

-   -   the proper fluidics around the MALDI ionisation surface,    -   the proper crystallisation on the MALDI ionisation surface,    -   the proper geometry of the port in relation to crystallisation,        evaporation, the incident laser beam etc,    -   the proper arrangement of conductive connections to the MALDI        ionisation surface for MALDI MS analysis.

WO 04297 (Karger et al) and WO 0247913 (Gyros AB) suggest to havemicrochannel structures in radial or spoke arrangement.

A number of publications referring to the use of centrifugal force formoving liquids within microfluidic systems have appeared during the lastyears. See for instance WO 9721090 (Gamera Bioscience), WO 9807019(Gamera Bioscience) WO 9853311 (Gamera Bioscience), WO 9955827 (GyrosAB), WO 9958245 (Gyros AB), WO 0025921 (Gyros AB), WO 0040750 (GyrosAB), WO 0056808 (Gyros AB), WO 0062042 (Gyros AB) and WO 0102737 (GyrosAB) as well as WO 0147637 (Gyros AB), WO 0154810 (Gyros AB), WO 0147638(Gyros AB), and WO 0146465.

See also Zhang et al, “Microfabricated devices for capillaryelectrophoresis—electrospray mass spectrometry”, Anal. Chem. 71 (1999)3258–3264) and references cited therein.

Kido et al., (“Disc-based immunoassay microarrays”, Anal. Chim. Acta 411(2000) 1–11) has described microspot immunoassays on a compact disc(CD). The authors suggest that a CD could be used as a continuous samplecollector for microbore HPLC and subsequent detection for instance byMALDI MS. In a preliminary experiment a piece of a CD manufactured inpolycarbonate was covered with gold and spotted with a mixture ofpeptides and MALDI matrix.

OBJECTS OF THE INVENTION

-   -   A first object is to provide improved means and methods for        transporting samples, analytes including fragments and        derivatives, reagents etc in microfluidic devices that are        capable of being interfaced with a mass spectrometer.    -   A second object is to provide improved microfluidic methods and        means for sample handling before presentation of a sample        analyte as an MS-analyte. Sub-objects are to provide an        efficient concentration, purification and/or transformation of a        sample within the microfluidic device while maintaining a        reproducible yield/recovery, and/or minimal loss of precious        material.    -   A third object is to provide improved microfluidic methods and        means that will enable efficient and improved presentation of        the MS-sample/MS-analyte. This object in particular applies to        MS-samples that are presented on a surface, i.e. an EDI surface.    -   A fourth object is to enable reproducible mass values from an        MS-sample that is presented on a surface, i.e. on an EDI        surface.    -   A fifth object is to provide improved microfluidic means and        methods for parallel sample treatment before presentation of the        analyte to mass spectrometry. The improvements of this object        refer to features such as accuracy in concentrating, in chemical        transformation, in required time for individual steps and for        the total treatment protocol etc. By parallel sample treatment        is meant that two or more sample treatments are run in parallel,        for instance more than five, such as more than 10, 50, 80, 100,        200, 300 or 400 runs. Particular important numbers of parallel        samples are below or equal to the standard number of wells in        microtiter plates, e.g. 96 or less, 384 or less, 1536 or less,        etc    -   A sixth object is to provide a cheap and disposable microfluidic        device unit enabling parallel sample treatments and having one        or more MS-ports that are adapted to a mass spectrometer.

SUMMARY OF THE INVENTION

The present inventors have recognized that several of theabove-mentioned objects can be met in the case inertia force is used fortransportation of a liquid within a microfluidic device of the kinddiscussed above. This is applicable to any liquid that is used in themicrofluidic device, for instance washing liquids and liquids containingat least one of (a) the analyte including derivatives and fragmentsthereof, (b) a reagent used in the transformation of the sample/analyte,etc.

The present inventors have also recognized that one way of optimizing anEDI area within a microfluidic device is related to

-   -   (a) the design and/or positioning of a conducting layer in the        EDI area, and/or    -   (b) the importance of a conductive connection to the EDI area        for MS analysis. This kind of connection supports the proper        voltage and/or charge transport at the EDI area, for instance.

Improper conductive properties may interfere with the mass accuracy,sensitivity, resolution etc.

Conductive and non-conductive properties shell refer to the property ofconducting electricity.

A first aspect of the invention is thus a method for transforming aliquid sample containing an analyte to an MS-sample containing anMS-analyte and presenting the MS-sample to a mass spectrometer. Themethod is characterized in comprising the steps of:

-   -   (a) applying the liquid sample to an inlet port of a covered        microchannel structure of a microfluidic device,    -   (b) transforming the liquid sample to an MS-sample containing        the MS-analyte within the microchannel structure, and    -   (c) presenting the MS-analyte to the mass spectrometer.

A further characteristic feature of this aspect is that transport ofliquid within the microchannel structure is performed by the applicationof inertia force. Inertia force may be the driving force in only a partof the microchannel structure or the whole way from an inlet port to anMS-port and/or to any other outlet port. It is believed that the mostgeneral and significant advantages of using inertia force will beaccomplished in so called transporting zones, i.e. between zones havingpredetermined functionalities, or for overcoming or passing throughvalve functions within a microchannel structure (capillary junctions,hydrophobic breaks etc). See below. The MS-port typically has aconductive connection for MS analysis.

At the priority date the most important inertia force for microfluidicdevices is centrifugal force. In other words a force that causes outwardradial transportation of liquid by spinning a disc in which the liquidis located within microchannel structures that are oriented radially(spinning is around an axis that is perpendicular to the plane of thedisc). Inertia force caused by other changes of direction and/ormagnitude of a force can be utilized.

The first aspect also includes the corresponding mass spectrometricmethod, i.e. the same method together with the actual collection of amass spectrum and analysis thereof, for instance in order to gainmolecular weight and structure information about the analyte.

The first aspect is further defined as discussed below for themicrofluidic device as such and for the individual steps.

A second aspect of the invention is a microfluidic device containingone, two or more microchannel structures containing an inlet port, anMS-port and a flow path connected to one or both of the ports. Thedevice may be disc-formed or otherwise provide a planar form. Thecharacteristic feature is that the microchannel structures are orientedradially in an annular/circular arrangement. Thus each microchannelstructure extends in a radial direction with an inlet port at an innerposition and an outlet port such as an MS-port, at an outer peripheralposition. The MS-port typically has a conductive connection as discussedabove. The features discussed below further define this aspect of theinvention.

A third aspect of the invention is a microfluidic device comprising aplurality of covered microchannel structures as defined herein and witheach microchannel structure having an MS-port comprising an EDI area inwhich there is a conducting layer (layer I). This aspect of the presentinvention comprises a number of subaspects having the commoncharacteristic feature that there may be a conductive connection tolayer (I) of each individual EDI area, as discussed above. There arealso features that are distinct for each subaspect.

-   -   A first subaspect is further characterized in that layer (I) of        each EDI area is part of a continuous conducting layer that is        common for two or more up to all of the EDI-areas.    -   A second subaspect is further characterized in that in each EDI        area there is a non-conducting layer (layer II) between        layer (I) and the surface of the EDI area. Layer (II) in each        EDI area may be part of a continuous non-conducting layer that        is common for two or more up to all of the EDI-areas.    -   A third subaspect is further characterised in that each MS-port        has an opening that is restricted by a lid which is common for        and covers a number of microchannel structures. The lid may have        a conducting layer that at least embraces the openings that are        present in the lid. The conducting layer may be continuous in        the sense that it covers at least the areas around and between        the openings of two or more up to all of the MS-ports. This        layer may have a conductive connection as discussed above.    -   A fourth subaspect is similar to the third subaspect in the        sense that there is a lid covering at least a part of each        microchannel structures. In this subaspect the lid also covers        or restricts the openings of the MS-ports and is removable to an        extent that enables exposure of the opening in each MS-port, for        instance exposing the surfaces of EDI areas. For EDI ports the        removal will facilitate irradiation and the        desorption/ionisation of the MS-analyte. The removal may also        facilitate evaporation of volatile components.        The Sample

The sample applied to an inlet port may contain one or more analytes,which may comprise lipid, carbohydrate, nucleic acid and/or peptidestructure or any other inorganic or organic structure. The sampletreatment protocol to take place within the microchannel structuretypically means that the sample is transformed to one or more MS-samplesin which

-   (a) the MS-analyte is a derivative of the starting analyte and/or-   (b) the amount(s) of non-analyte species have been changed compared    to the starting sample, and/or-   (c) the relative occurrence of different MS-analytes in a sample is    changed compared to the starting sample, and/or-   (d) the concentration of an MS-analyte is changed relative the    corresponding starting analyte in the starting sample, and/or-   (e) sample constituents, such as solvents, have been changed and/or    the analyte has been changed from a dissolved form to a solid form,    for instance in a co-crystallised form.

Item (a) includes digestion into fragments of various sizes and/orchemical derivatization of an analyte. Digestion may be purely chemicalor enzymatic. Derivatization includes so-called mass tagging of eitherthe starting analyte or of a fragment or other derivative formed duringa sample treatment protocol, which takes place in the microchannelstructure. Items (b) and/or (c) include that the sample analyte has beenpurified and/or concentrated. Items (a)–(d), in particular, apply toanalytes that are biopolymers comprising carbohydrate, nucleic acidand/or peptide structure.

The sample is typically in liquid form and may be aqueous.

The sample may also pass through the microchannel structure withoutbeing changed. In this case the structure only provide a proper form fordosing of the analyte to the mass spectrometer.

FIGURES

FIGS. 1–3 illustrate various microchannel structures that have anMS-port.

FIG. 4 illustrates an MS-port in form of an electrospray (sideview).

FIGS. 5 a–f illustrate various design and positions of the conductinglayer (I) in MS-ports containing an EDI area (cross-sectional sideviewof two ms ports). The microfluidic device is fabricated in a planarsubstrate.

FIG. 6 illustrates an arrangement around EDI MS-ports with layer (I) andconductive connections (transparent lid, seen from above).

FIGS. 7 a–b illustrate a variant of an EDI-port with a transparent lid(seen from above and in a cross-sectional sideview, respectively).

DETAILED DESCRIPTION OF THE INNOVATIVE MICROFLUIDIC DEVICE

The Microfluidic Structure

The microfluidic device comprises one or more microchannel structureshaving an inlet port for application of a liquid sample and an MS-portfor release and presentation of an MS-analyte to a mass spectrometer.These kinds of ports may coincide in a microchannel structure. There mayalso be separate inlet ports for application of solvents and reagentsand separate outlet ports or waste chambers/cavities for withdrawal ofother components that are added and/or produced in the structure. Two ormore microchannel structures may have common inlet ports. Depending onthe particular design of the device some of the ports may be closedduring the sample treatment but opened later on, for instance in orderto enable proper release and presentation of the MS-analyte.

The distance between two opposite walls in a channel is typically ≦1000μm, such as ≦100 μm, or even ≦10 μm, such as ≦1 μm. Functional channelparts (chambers, cavities etc) typical have volumes that are ≦500 μl,such as ≦100 μl and even ≦10 μl such as ≦1 μl. In important variantsthese volumes may be ≦500 nl such as ≦100 nl or ≦50 nl. The depths ofthese parts may be in the interval ≦1000 μm such as ≦100 μm such as ≦10μm or even ≦1 μm. The lower limits (width and depth) are alwayssignificantly greater than the largest of the reagents and analytes(including fragments and derivatives) that are to be transported withinthe microchannel structure. The lower limits of the different channelparts are typically in the range 0.1–0.01 μm. The aspect ratio (depth towidth) may be ≧1 or ≦1 in all parts or in only a part of a microchannelstructure.

Preferred microfluidic devices typically comprise one, two or more,preferably more than 5, microchannel structures fabricated wholly orpartly in the surface of a planar substrate. In the preferredmicrofluidic devices of the invention, the side of the substrate inwhich the microchannels are located (microchannel side) may be coveredby a lid comprising remaining parts, if any, of the microchannelstructure. When the lid is properly mated to the upper side of thesubstrate, parts of the microchannel structures in the lid, if any,match the structures in the microchannel side thereby completing themicrochannel structures of the device. The lid will prevent or minimiseundesired evaporation of liquids as well as facilitate transport ofliquids.

Each microchannel structure preferably extends in a common plane of theplanar substrate material. In addition there may be extensions in otherdirections, primarily perpendicular to the common plane. Such otherextensions may function as sample or liquid application areas orconnections to other microchannel structures that are not located in thecommon plane, for instance.

The microfluidic devices may be disc-formed and have various geometries,with the circular form being the preferred variant (CD-form). Othervariants of discs may have an axis of symmetry that is at least 3- or atleast 6-numbered.

On devices having circular forms or an axis of symmetry as mentioned inthe previous paragraph, each microchannel structures may be orientedradially around a central axis with an intended flow direction for eachstructure from an inner application area (inlet port) towards theperiphery of the disc. The arrangement may be in form of one or moreconcentric circles (annular/circular arrangements). According to thefirst aspect of the invention the liquid is transported by inertiaforce, for instance centrifugal force, in at least a part of amicrochannel structure. Examples of other ways of transportation are bycapillary action, hydrodynamically, electrokinetically etc. Thesealternatives may also be combined with inertia force in line with whathas been discussed for the first aspect of the invention.

Each microchannel structure comprises one or more channels in themicroformat. The channels may comprise chambers/cavities that are in themicroformat. Different parts of a structure may have different discretefunctions. In addition to the channel parts mentioned above (inlet port,MS-port, transportation conduit/channel), there may be one or morechannel parts that function as

-   (a) application zone/port for reagents and liquids other than sample    liquid (second inlet port),-   (b) additional MS-ports,-   (c) reaction zone, for instance for derivatization of an analyte    discussed above (digestion, tagging etc).-   (d) pressure creating zone (for instance hydrostatic pressure),-   (e) volume defining zone,-   (f) mixing zone,-   (g) zone for separating and/or concentrating and/or purifying the    analyte or a derivative or fragment thereof, for instance by    capillary electrophoresis, chromatography and the like,-   (h) waste conduit/chamber/cavity (for instance in the form of an    outlet port),-   (i) zone for splitting a liquid flow, etc.

These kinds of zones may be present as distinct chambers or conduitsthat may have a cross-sectional dimension that differs from a precedingand/or a subsequent part of the microchannel structure.

Splitting may be located at the inlet so that a starting sample isdivided in several aliquots, each of which is processed in parallelwithin a structure.

Except for the presence of an MS-port this kind of microchannelstructures have been described in a number of previous patentpublications. See the background publications discussed above.

Between parts having different functions there may be valves that can beovercome by increasing the force driving the liquid. For variantsutilizing spinning, this may for instance be accomplished by increasingthe spinning and/or utilizing pressure built up within the structure dueto addition of a new portion of liquid combined with spinning. See forinstance WO 0040750 (Gyros AB) and WO 0146465 (Gyros AB). Valves may bebased on capillary junctions (WO 9807019 (Gamera Bioscience)) orhydrophobic breaks (WO 9958245 (Gyros AB) or on thermic properties ofthe valve material. The latter kind of valves may be illustrated by socalled sacrificing valves (WO 9853311 (Gamera Bioscience)) for instancecontaining a plug of wax-like material, or reversible valves, forinstance containing a thermoreversible polymer in the form of a plug (WO0102737 (Gyros AB)).

One kind of versatile microchannel structures used according to theinvention comprise a zone in which separation and/or concentrationand/or a purification of the analyte or an analyte-derived entity cantake place. This zone is located either before or in the MS-port.Examples of analyte-derived entities are fragments and derivatives ofthe analyte. This kind of functionality may be particularly importantfor samples containing low concentrations of analytes, complex mixturesof analytes or high concentrations of interfering substances that maynegatively affect the resolution and/or sensitivity of the MS-analytewhen analyzed by mass spectrometry. Separation and/or concentrationand/or purification of the sample analyte or analyte-derived entitiescan be accomplished according to similar principles as typicallyemployed in the life science area, i.e. separations based on sizeexclusion and/or on differences in binding to a ligand structure areapplicable. Accordingly, this kind of channel part may contain aseparation medium that is capable of binding the analyte or ananalyte-derived entity but not to the contaminants, or vice versa. Theseparation medium is typically in particle/bead form, or attached on thesurface of the separation zone or in the form of a monolithic plug thatpermits through flow. If the analyte or the analyte-derived entitybecomes bound, a liquid having the proper desorption characteristics forthe bound entity is subsequently allowed to pass through the chamberwhereupon the bound entity is released and transported downstream. Thistransport may be directly to the MS-port or to a zone in which a furtherpreparation step is accomplished. Washing steps may be inserted betweenthe sample liquid and the desorption liquid. The separation medium maybe soluble or insoluble during the binding step. Soluble separationmedia are typically insolubilized after binding according to principleswell-known in the field of macrosopic separations.

Binding to the separation medium may involve formation of covalent bondsor encompass affinity binding. Binding of covalent nature for thispurpose is typically reversible, for instance by thiol-disulfideexchange, such as between a thiol-containing analyte or analyte-derivedentity and a separation medium containing a so called reactivedisulfide, or vice versa. Affinity binding, including adsorption, can beillustrated with:

-   (a) electrostatic interaction that typically requires that the    ligand and the entity to be bound have opposite charges,-   (b) hydrophobic interaction that typically requires that the ligand    and the entity to be bound comprises hydrophobic groups,-   (c) electron-donor acceptor interaction that typically requires that    the ligand and the entity to be bound have an electron-acceptor and    electron-donor group, respectively, or vice versa, and-   (d) bioaffinity binding including other kinds of binding in which    the interaction is of complex nature, typically involving a mixture    of several different kinds of interactions and/or groups.

Ion exchange ligands may be cationic (=anion exchange ligands) oranionic (=cation exchange ligands). Typical anion exchange ligands havea positively charged nitrogen, the most common ones being primary,secondary, tertiary or quarternary ammonium ligands, and also certainamidinium groups. Typical cation exchange ligands are negatively chargedcarboxylate groups, phosphate groups, phosphonate groups, sulphategroups and sulphonate groups.

Bioaffinity binding includes that the analyte or the analyte-derivedentity is a member of a so-called bioaffinity pair and the ligand is theother member of the pair. Typical bioaffinity pairs are antigen/haptenand an antibody/antigen binding fragment of the antibody; complementarynucleic acids; immunoglobulin-binding protein and immunoglobulin (forinstance IgG or an Fc-part thereof and protein A or G), lectin and thecorresponding carbohydrate, etc. The term “bioaffinity pair” includesaffinity pairs in which one or both of the members are synthetic, forinstance mimicking a native member of a bioaffinity pair.

If the analytes in a sample have peptide structure or nucleic acidstructure or in other ways have a pronounced hydrophobicity, theseparation medium may be of the reverse phase type (hydrophobic)combined with using desorption liquids (eluents) that are organic, forinstance acetonitrile, isopropanol, methanol, and the like. Depending onthe particular sample and the presence of analytes or analyte-derivedentities, which have a common binding structure, a group-specificseparation medium may be utilized for the kind of separations discussedabove. The separation medium may thus, like a reverse phase adsorbent,result in an MS-sample that has a reduced concentration of salt, i.e. indesalting.

In each microchannel structure there may be two or more separationszone. In this case the zones typically seaparate according to differentprinciples such as size and charge. For amphoteric substances such asproteins and peptides the latter principle may be illustrated withisoelectric focusing.

By using a separation zone it is possible to concentrate the sample suchthat the concentration of an analyte or an analyte-derived entity in thedesorption liquid after passage of the separation medium is higher thanin the starting sample. The increase be be with a factor >10⁰ and maytypically be found in the interval 10¹–10⁶, such as 10¹–10⁴.

As already mentioned a separation zone may be combined with zones forderivatization. There may also be microchannel structures that have aderivatization zone but no separation zone.

FIG. 1 illustrates a microchannel structure that comprises (a) an inletport (1) for liquids including the sample liquid, (b) an MS-port (2)comprising for instance an EDI area that may be opened or closed, (c) aflow conduit (3) between the inlet port (1) and the MS-port (2). Theflow conduit (3) may have a zone (4) containing an adsorbent forseparation/concentration. If there are several microchannel structure ina device there may be a common application area/channel with openingsfor the inlet ports (not shown). The MS-port may be an EDI MS-port, aneletrospray MS-port.

The use of the structure of FIG. 1 is as indicated. By using spinningfor liquid transportation into an open form of the MS-port, aqueousliquids, for instance the sample or the washing liquids, may leave theport as small drops by the centrifugal force while liquids having alower vapour pressure may evaporate leaving the MS-analyte in the port,e.g. at a lower spinning rate.

FIG. 2 illustrates another variant of a suitable microchannel structure.It has two inlet ports (5,6) that may be used for application of sample,washing liquids and desorption liquid. One of the inlet ports (5) isconnected to an application area/channel (7) that may be common toseveral microchannel structures in the same device. This first inletport (5) is connected to one of the shanks (8) in a U-shaped channelpart via the application area/channel (7). The other inlet port (6) isconnected to the other shank of the U. In the lower part of the U thereis an exit conduit (9) leading to an MS-port (10). In the channel (11)between the exit conduit (9) from the U and the MS-port (10) there maybe a zone (12) containing a separation medium. From the MS-port (10)there may be a waste channel (13) leading to a waste space (14) that maybe common for several microchannel structures in the same device. Theremay be a valve function, for instance in the form of a hydrophobicbreak, in the exit conduit (9).

FIG. 3 illustrates another alternative of a microchannel structure whichcomprises a separate sample inlet port (14), an MS-port (15) andtherebetween a microchannel structure that may be used for samplepreparation. In this variant there is a volume-defining unit (16)between the two ports (14,15) with an over-flow conduit (17). At thelower part of the volume-defining unit (16) there is a first exitconduit (18) leading to one of the shanks (19) of a U-shaped channelpart. The other shank (20) of this U may be connected to an inlet port(21) for washing and desorption liquids. At the lower part of theU-shaped channel part there may be a second exit conduit (22) leadinginto one of the shanks (23) of a second U-shaped channel part. The othershank (24) may be connected to a waste channel (25 b) that after a bent(26) may end in a waste chamber (25 a). At the lower part of this secondU-formed channel part there may be a third exit conduit (27) leadinginto the MS-port (15) that may contain an EDI area or an electrosprayunit. In order to control the flow in the structure, valve functions arepreferably located in the first exit conduit (18), for instanceimmediately downstream the volume-defining unit (16), possibly also inthe second exit conduit (22), for instance immediately after the firstU-shape, and in the third exit conduit (27), for instance immediatelyafter the second U-shaped channel part. The valves may be of the typesdiscussed above with preference for hydrophobic breaks. A suitableadsorbent (28) as discussed above may be placed in the shank (23) of thesecond U-shaped channel part and may also function as a valve. In casethe adsorbent is in the form of particles they are preferably kept inplace by a constriction of the inner walls of the conduits.

The structure presented in FIG. 3 is adapted for transporting the liquidwith centrifugal forces, i.e. with the structure present in a disc andoriented radially outwards from the centre of the disc. At start thevolume-defining unit (16) is filled up somewhat above the over-flowchannel (17). By overcoming a valve function located in the first exitconduit (18), the liquid will pass into the first U-shaped channel partand down through the adsorbent where the analytes are captured. Theremaining liquid containing non-analyte components will pass out intothe waste channel (25 b). In the next step, washing liquids may beapplied through the inlet port (21), i.e. through the second shank (20)of the first U-shaped channel part or via the same inlet port (14) asthe sample. Also these liquids will pass out into the waste channel (25b). Subsequently, a desorption liquid is applied through either of thetwo inlet port (14,21) and allowed to pass through the valve function inthe third exit conduit (27). The desorption liquid containing releasedanalyte or analyte-derived entities is passed downstream, for instanceinto the MS-port (15). The operations are preferably carried out whilespinning the disc. If the valves are in the form of hydrophobic breaksthey can be passed by properly adapting the g-forces, i.e. by thespinning. By properly balancing the hydrophilicity/hydrophobicity of aliquid, passage or non-passage through a valve may be controlled withoutchanging the spinning speed. This is illustrated by utilizing ahydrophobic break as the valve in the third exit conduit (27) combinedwith utilizing water-solutions as samples and as washing liquids andliquids containing organic solvents as desorption liquids. In thealternative, valves that are opened by external means can be used. Byplacing the outlet to the first exit conduit (18) at a distance abovethe lowest part of the volume-defining unit (16) particulate matters, ifpresent in the sample, will sediment and be retained in thevolume-defining unit (16) when it is emptied through the first exitconduit (18).

Calibrator areas (29) are shown in each of FIGS. 1–3. Each calibratorarea may be connected to a common area for application of calibrator.

The size of a volume-defining unit depends on the sample, reagents used,washing etc. and the requirement the sensitivity of the massspectrometer sets for concentrating an analyte or an analyte-derivedentity. Typical volumes of channel parts that have specific functionsare in the range of 1 nl to 1000 μl, mostly below 1 μl such as below 500nl or even below 100 nl such as below 25 or 10 nl (volume defining unit,reactor part, separation part etc). Application of aliquots of a sampleto the same inlet port may replace the need for a larger volume definingunit.

These kind of flow systems has been described in WO 0040750 (Gyros AB)and WO 0146465 (Gyros AB) which are hereby incorporated by reference.

In certain variants the inlet port for the sample and the MS-port maycoincide. In this case the MS-port preferably comprises the surface onwhich the analyte can be collected (adsorbed). Remaining liquid andwashing liquids, if used, are passed into the microchannel structurethat then will function as a waste channel and possibly contain aseparate outlet port particularly adapted for wastes and the like, or awaste chamber. In order to accomplish a concentrating and/or separatingeffect the surface may expose structures selectively binding/capturingthe analyte as discussed above. This variant also encompasses that theremay be a separate inlet port for washing and desorption liquids andmicrochannel part communicating with the combined sample and MS-port.

The MS-port

The invention the MS-port typically has conducting properties. Theconducting part may be present in an EDI area or a nozzle suitable forelectrospray, for instance a nanospray, or in any other form device thatis used to present a sample to a mass spectrometer. An electrospraynozzle provides an orifice for instance in the form of a tip with athrough-passing hole. Various kinds of sample presentation devices havebeen described in the publications discussed above.

There may be a valve in the microchannel before its inlet to theMS-port.

The term conducting material includes semi-conducting material, althoughmaterials having a conductivity that is larger than silicon or largerthan germanium are preferred. A typical conducting material comprise

-   -   (a) metals such as copper, gold, platinum etc,    -   (b) conducting polymers including polymers that are conducting        as such, and conducting composites containing a non-conducting        polymer and a conducting material such as a metal or a        conducting polymer,    -   (c) other conducting composites, etc.        Electrospray Ionisation MS-Ports

FIG. 4 illustrates an MS-port suitable for electrospray ionisation in amass spectrometer. This kind of port may be located where an MS-port hasbeen indicated in any of the structures given in FIGS. 1–3. TheMS-analyte may thus be collected in an MS-port comprising a collectionzone (30), which zone is in fluid communication via the electrosprayconduit (31) with the outlet orifice (32). The electrospray conduit maybe in the form of a tip. The MS-analyte is entering via conduit (32). Asindicated in FIG. 4, orifices of the electrospray tip are preferablypositioned on the edge of a disc. Typical disc-forms have been discussedabove. In use an electrospray orifice is matched to the sampling orificeof a mass spectrometer and liquid in the electrospray tip (31) issprayed into the mass spectrometer. In a preferred variant the disc iscircular. The arrangement of the electrospray tips is preferably annulararound the axis for spinning during preparation of the sample. The tipsare preferably located in the edge of the disc and provide a radialspray direction. In the alternative the annular arrangement may by in aflat side of the disc with a spray direction out of the plane of theside and preferably also with a component that is directed radially.Annular arrangements preferably in the edge of a circular disc willsimplify accurate positioning of the electrospray direction relative tothe sample application opening of a mass spectrometer.

Electrospray suitable for electrospray ionization mass spectrometry (ESIMS), for instance adapted to the nanospray format, is mostly formed incapillaries made of glass or fused silica, or polymer material likesilicon. The tubings are typically of cylindrical geometry with tipinternal diameters in the 5–20 μm range. The word nanospray means thatthe liquid transferred out of the tubing is in the nanoliter per minuterange. Suitable rates for transfer of liquid to the mass spectrometercan be found in the interval of 1–1000 nl/min, e.g. in the interval10–500 nl/min. By infusion (no external force), only a few nanolitersper minute (5–25 nl/min) is transported out of the tubing while withapplied external pressure 50–500 nl/min is more common.

A liquid solution suitable for ESI MS analysis consist of an organicsolvent:water mixture including a lower concentration of acid or base.The composition of the solvent is important especially with regard tosurface tension and conductivity. A low surface tension and conductivityis desirable to obtain an efficient desolvation and ionization processas well as a stable spray. If the sample is dissolved in water only, aso-called make-up solvent is preferably added (external delivery) to aidin the above mentioned process. A make-up solvent is typicallyconfigured co-axially (sheat-flow) around the nanospray tip. A make-upgas (typical N₂) is sometimes added (e.g., co-axially) as to aid in thedesolvation process. Creation of a suitable liquid composition of theMS-sample may also be part of the sample preparation process takingplace upstream the MS port in other parts of a microchannel structure.

The tip geometry is important as to obtain a stable spray. Preferablythe tip is pulled from the cylindrical tubing whereby the tip becomesoblong with a conical shape. The outer diameter of the tubing near theorifice of the tip then becomes of similar dimension as the internaldiameter.

In order to induce a spray from the capillary (towards the inlet of themass spectrometer) a voltage has to be applied on the electrospray tip.Therefore the tip has to be made conductive. Different kind of metalscan be deposited by different techniques onto the tip (or part of thetubing). Important aspects here regard the stability (life-time) of themetallized tip since the voltage applied as well as different solventsaffects its stability. Other possibilities also exist than metalization,e.g., an electrode can be inserted into the tip whereby a voltage can beapplied to induce electrospray. Another alternative is to make the tipin a material comprising any of the above-mentioned conductingmaterials. Typical voltages used in nanospray range between 500–2000volts.

Typical electrospray nozzles are available from a number ofmanufacturers, for instance New Objective, MA, U.S.A. A variant that isbelieved to have advantages for microfluidic devices is presented in WO0247913 (Gyros AB). See also WO 9704297 (Karger et al), U.S. Pat. No.5,969,353 (Hsieh) and U.S. Pat. No. 6,110,343 (Ramsey et al) discussedabove.

EDI MS-ports

The MS-port may also be used for EDI-MS and will then contain anEDI-area. Upward and downward directions as used in the context of EDIareas refer to the directions defined in the figures irrespective of howthe area is positioned in a mass spectrometer.

The term “EDI area” encompasses the surface of the area as well as anypart of the device, which is straight under the surface.

EDI MS ports may be adapted to anyone of the different EDI massspectrometry variants, for instance Time of Flight (TOF), Quadropole,Fourier-Transformed Ion Cyclotron Resonance (FT-ICR), ion trap etc.

EDI ports need a free opening for the release of the ions created duringdesorption/ionisation. This means that the opening typically is placedstraight above the surface of an EDI area and has an area that should becoaxial with and covering the surface. This includes that the openingmay be closed during the sample treatment within the microfluidic devicebut subsequently opened to enable irradiation and desorption/ionisationand possibly also evaporation of solvents. If an IDI principle is usedthe opening should also provide space for the incident irradiation.

An EDI area may in principle have any geometric form although preferredforms should be as compact as possible. Regular forms, such as squaresand square-like forms, and rounded forms, such as circular andcircle-like forms. The size of an EDI area preferably is the same as acircle with a diameter in the interval of 25–2000 μm. For IDI there maybe advantages if the cross-sectional area of the incident beam is ableto encompass the complete surface of an IDI area or as much as possible,for instance more than 25% or more than 50%.

An EDI area comprises a conducting layer (layer I), for instance a metallayer of copper, gold, platinum, stainless steel etc or a layer of anyother conducting material of the kinds discussed above. Layer (I) ismany times essentially planar and may coincide with the surface of theEDI area or be parallel thereto. The complete area from the lowest partto the most upper part may be made of conducting material, i.e.correspond to layer (I). In the case the microfluidic device comprisesmore than one microchannel structure with an EDI MS-port, layer (I) ofone EDI area may extend into and encompass layer (I) in two or more ofthe other EDI areas, with preference for all of them. Layer (I) of allEDI areas of a device may be part of a common conducting layer, whichmay be essentially planar and possibly with depressions corresponding tothe EDI areas and/or to other parts of the microchannel structures ofthe innovative device. The exact geometric shape of layer (I) outsidethe MS-port may differ depending on the particular device and practicalways of its manufacture. For instance a common conducting layer may havean annular form in case the MS-ports are annularly arranged, i.e. onlybe present in EDI areas of a certain distance from a the centre of thearrangement.

In one innovative variant, there is a non-conducting layer (layer (II)),which covers the conducting layer (I). Layer (II) in one EDI area mayextend into and encompass layer (I) in two or more of the other EDIareas as described for layer (I).

In another innovative variant the device have a conducting layer (III)positioned above the common plane defined by the surface of each EDIarea of a device. Layer (III) has openings matching the surfaces of theEDI areas and permitting irradiation of the EDI surfaces and escape ofions produced through the openings.

These innovative variants of EDI areas are schematically illustrated inFIGS. 5 a–f, each of which shows a cross-sectional view across the EDIareas of two EDI MS-ports in a microfluidic device according to theinvention. The EDI surfaces are referenced as (51) and the EDI areas as(52) within the dotted vertical lines). Each EDI port comprises the EDIarea plus the corresponding depression. The conducting layers (54) arehatched. It is apparent that each EDI area comprises a conducting layer(I) (53).

FIG. 5 a shows a common conducting layer (54) at the bottom of thedevice which layer encompasses layer (I) (53) of each EDI area (52). Anon-conducting layer (II) (55) is placed between layer (I) (53) and theEDI surface (51). FIG. 5 b shows a variant, which is similar to thevariant in FIG. 5 a, but the common conducting layer is embedded withinthe material from which the device is fabricated. Layer (II) (55) ispresent. In FIG. 5 c there is a common conducting layer (54) comprisingthe upper surfaces of the EDI areas. In FIG. 5 d there is no commonconducting layer. Layer (I) is in the upper surfaces of the EDI areas.The different layers (I) (53) are isolated from each other. FIGS. 5 eshows a variant in which there is a continuous conducting layer (54)above layer (I) (53) of the EDI areas. This conducting layer (54) hasopenings (56) corresponding to the openings of each MS-port and may bethe surface of the upper or lower side of a lid covering themicrochannel structure (the lid is not shown). FIG. 5 f shows a variantin which there is a common continuous conductive layer comprising layer(I). Layer (I) corresponds to the EDI surfaces. The continuous layeralso encompasses the walls of the depressions in the EDI ports.

In one variant all the material of the body in which the microchannelstructures are fabricated is the same as in layer (I), i.e. there may beno non-conducting material present, except for the lid.

FIG. 6 illustrates an arrangement for EDI MS-ports on a circular disc(with a transparent lid), in which layer (I) (34) of each EDI surfacehas a conductive connection (35) with a peripherial conductive layer(36) at the edge of the disc. In the variant shown in this figure eachmicrochannel structure (37) extends upstream to an inlet port (38).

FIGS. 7 a–b illustrate an EDI MS-port which the opening to the EDIsurface is defined by a hole (39) in a lid (40) which in this case istransparent. One can see the incoming microchannel (41), which opens toa circular depression (42) with a diameter, which is less than thediameter of the hole (39). Layer (I) (43), EDI area (44, between thedotted lines), EDI surface (45) are shown. The conductive layer extendsfrom layer (I). This design in which the MS-port provides an openingwhich is greater than the EDI area will facilitate for an incident beamto cover any spot of the EDI surface.

A conductive layer per se may function as a conductive connection orthere may be distinct connections (35) to layer (I). See FIG. 6.

A lid used to cover the microchannel structure may also cover the EDIareas or restrict them from exposure to the ambient atmosphere. In thiscase there may be advantages if the lid is removable at least around theEDI areas. Thus after treatment in upstream parts of the microchannelstructure, the EDI areas can be exposed for evaporation of solvents thatmay be retained thereon or for irradiation in order to accomplishdesorption/ionisation of MS-analyte molecules.

The Method Steps of the First Aspect of the Invention.

When the innovative device is used, the necessary reagents and/or thesample including the analyte are applied to the appropriate inlet ports(application areas) and transported downstream in the structure by anapplied liquid flow or transportation mechanism as discussed above. Theliquid flow or transport may be paused when a reagent and/or an analytehave reached a predetermined part in which the sample is subjected to acertain procedure, for instance capillary electrophoresis in aseparation part, a chemical reaction in a reaction part, selectiveadsorption in a concentrating part, detection in a detection part,evaporation and/or crystallization in an EDI MS-port, collection of theappropriate liquid for electrospray ionisation in an electrosprayionisation MS-port, etc.

During transport through a microchannel structure the solventcomposition may be changed to fit the particular kind of MS-port used.In the case the MS-port is an EDI MS-port and the microchannel structurecontains a separation medium, an EDI matrix may be (a) included in thedesorption liquid or in a subsequent liquid passing through at least apart of the microchannel structure, (b) predispensed to the EDI surfaceor dispensed after the analyte has been deposited on the surface, or (c)introduced via a separate microchannel downstream the separation medium.There may also be included substances that facilitate crystallization onthe EDI surface.

Calibration of the Mass Scale.

To ensure accurate mass determination, calibrator areas (spots)containing a compound of known molecular weight (standard) may presentin the proximity of the EDI MS-ports. Calibrator areas (29) are shown inFIGS. 1–3. Alternatively, the standards may be included in the sample oradded to the EDI area before desorption/ionisation (internalcalibrator). The choice of calibrator substance, its amount etc willdepend on its use as an external or internal calibrator, the MS-analyteand its concentration etc.

Material from which the Microfluidic Device is Manufactured.

The microchannel structures are typically fabricated in inorganic and/ororganic material, preferably plastics or other organic polymers. Thematerial may be conducting or non-conducting as already discussed.Certain parts of a microchannel structure may be metalized.

Suitable organic polymers may derive from polymerisation of monomerscomprising unsaturation such as carbon-carbon double bonds and/orcarbon-carbon-triple bonds. The monomers may, for instance, be selectedfrom mono-, di and poly/oligo-unsaturated compounds, e.g. vinylcompounds and other compounds containing unsaturation.

Another type of organic polymers that may fit are based on condensationpolymers in which the monomers are selected from compounds exhibitingtwo or more groups selected among amino, hydroxy, carboxy etc groups.The plastics contemplated are typically polycarbonates, polyamides,polyamines, polyethers etc. Polyethers include the corresponding siliconanalogues, such as silicone rubber.

The polymers of the plastics are preferably in cross-linked form.

The plastics may be a mixture of two or more differentpolymer(s)/copolymer(s).

At least a part of the microchannel structure may have a surface thathas been derivatised and/or hydrophilized, for instance by being coatedwith a non-ionic hydrophilic polymer according to the principlesoutlined in International Patent Publication WO 0147637 (Gyros AB). Thisalso includes functionalisation in order to introduce one or morestructures that are capable of interacting with the sample analyte orwith one or more of the reagents added. Surfaces may be made of copper,gold, platinum, stainless less etc, for instance by metallization, inorder to enable a desired derivatization or for providing a conductingsurface, for instance in an MS-port. Gold surfaces for instance may bederivatized by reaction with thiol-containing compounds that have adesired functionality, for instance hydrophilicity.

The optimal water contact angle for the surfaces within a structuredepends on the protocols to be carried out, the dimensions of themicrochannels and chambers, composition and surface tension of theliquids, etc. As a rule of thumb, at least one surface of themicrochannel structure (wall, bottom or top), should provide a watercontact angle that is ≦40° or ≦30°, such as ≦25° or ≦20°. These figuresrefer to values obtained at the temperature of use, primarily roomtemperature.

It is believed that the preferred variants of the inventive microfluidicdevices will be delivered to the customer in a dried state. The surfacesof the microchannel structures of the device therefore should have ahydrophilicity sufficient to permit the aqueous liquid to be used topenetrate the different parts of the channels of the structure bycapillary forces (self-suction). This of course only applies if a valvefunction at the entrance of the particular part has been overcome.

Best Mode

The best mass spectrometric results so far accomplished have been withthe variant described in example 4 below. It is believed that there areadvantages by going over to more complex fluidic structures asillustrated in FIGS. 2 and 3, and more complex designs of the EDIsurface and the channel outlets as illustrated in FIG. 7.

The invention is further defined in the appending claim and will now beillustrated with a non-limiting experimental part.

EXPERIMENTAL PART EXAMPLE 1

Gold at Different Positions in a CD

Charging of Gold patterning Sensitivity* substrate** No gold Poor YesGold on all sides Good No Gold on upper side Good No Gold on bottom sideGood Yes Isolated gold spots on the upper side Good Yes Gold spots onthe upper side. Every Good No spot being conductively connected contactwith the adapter plate through an individual gold string or a commongold area. *Good = sensitivity for a in-solution tryptic digest of BSAcomparable to the sensitivity obtained on a conventional stainless steeltarget **Charging is observed as significant mass shift (≧1 Da) uponrepeated laser desorption/ionization and/or loss of signal.

This table shows the results form a summary of experiments performed inorder to optimise the design of the CD-MALDI interface. Gold wassputtered at various positions of the CD and the MALDI characteristicswere studied for a tryptic digest of Bovine Serum Albumin (BSA). The CDwas placed on a metal adapter inserted into the ion source. The gold washence patterned in various ways to determine the importance ofelectrical contact between the MALDI ports and the adapter plate.

EXAMPLE 2

Testing of Crystallization on the MALDI Surface

Microfluidic device: The CD was fabricated of polycarbonate . Eachmicrochannel structure in the CD only contained an inlet port(uppstreams), the ms-port (downstreams) and a flow conduit between. Theinlet and ms-port consisted of open areas made by drilling holes in thelid before covering the CD with the lid, i.e., the open areas on the CDwas in contact with the surrounding atmosphere. Only a minor part of theflow conduit at the ms-port was in connection to the open area. Thewidth and the depth of the microchannel leading into the ms-port were100 μm and 40 μm, respectively. The open area of the ms-port had acylindrical geometry with a diameter of 300 μm (drilled hole) and depth70 μm., where the depth is the thickness of the lid. The bottom of theopen area, therefore, constituted of the upper surface of the CD (and aminor part of the microfluidic channel) while the walls surrounding theopen area, and restricting the dimension of the ms-port, was defined bythe hole in the lid. The CD was metallized with gold (gold-sputtering)only on the side opposite to the microchannel structures.

Experimental: 100 nl of a sample consisting of two peptides, AngiotensinII (Mw 1046.2) and Bradykinin (Mw 1060.2), 20 fmol/μl each, dissolved in50% isopropanol saturated with α-cyanohydroxycinnamic acid (+0.1%trifluoroacetic acid) was applied in the inlet hole by pipetting andtransported to the open area by spinning (500 rpm). The CD wasthereafter cut in half and the part containing the samples to beanalysed was fixed by metal-screws onto a MALDI target probe adapted tocontain on half of the CD. The probe was a Bruker standard target in the96 well format. The CD+ probe was then inserted into a Bruker BiflexMALDI time-of-flight (TOF) apparatus for mass spectrometry analysis.

Results:

The sample liquid was slowly transported out into the open area (500rpm). Once reaching the open area the solvent quickly evaporated andcrystallization started. Crystals could been seen as dark spots in theopen area of the ms-port. The volume of the ms-port was 5 nl while thesample applied was 100 nl. Since the volume transported out into theopen area per time unit was less than 5 nl and solvent evaporation pertime unit was faster than the incoming volume no overflooding in thems-port was taking place. Therefore, the sample volume applied can farexceed the volume of the ms-port whereby the sample can be concentratedtherein.

A high mass resolution was obtained since the peptide peaks wereisotopically resolved. The peptide masses deviated slightly (less then 1Dalton) from their theoretical values, but no calibration was performed.Also, the detection sensitivity has to be considered high since lowfemtomoles of peptides were detected (signal-over-noise ratio of 10)which is typically seen only in optimized MALDI TOF analysis.

EXAMPLE 3

Planar CD and Structured Removable Lid.

This example shows a planar CD in combination with a lid in which themicrofluidic structures are present. The structured lid was achievedthrough casting Memosil (Hereaus, Germany) against a nickel-coatedmaster. The microfluidic structure employed in this example is shown inFIG. 2.

The structured lid is attached to the CD by adhesion forces. The surfacefacing the lid should be hydrophilic as the presented invention utilizescapillary action to fill the microfluidic structures. This is especiallyimportant as the moulded lid, being a type of silicon rubber ishydrophobic.

The upper side of the CD was covered with gold using a DC Bias magnetronsputtering method (1*10–5 torr, Ar plasma and titan as adhesion layer)and made hydrophilic according to the following procedure; The goldsputtered side was cleaned by rinsing with ethanol, followed by anoxygen plasma treatment (Plasma Science PSO500,). After plasma cleaninga self-assembled monolayer (SAM) of hydroxylthiol was formed on the goldsurface. The hydroxylthiol was 11-mercapto-1-undecanol (Aldrich,Milwaukee, Wis.) and used at a concentration of 2 mM in degassedethanol. To obtain a well-organized SAM, the gold sputtered disc wasimmersed in the thiol solution over night. After the thiol adsorptionthe CD was sonicated in ethanol for ca 2 min.

The lid, containing the Microfluidic channels, was attached to the CD byadhesion forces. A second piece of polymeric material was mounted at aposition of 180° from the structured lid as a counterbalance. Reversedphase beads (Source 15 RPC, Amersham Pharmacia Biotech, Sweden) with adiameter of 15 μm were packed into the individual structures using thefilling port present in the common distribution channel. The slurry,containing the beads, was drawn into the individual channels bycapillary action. Eighteen parallel reversed phase columns were formedwhen the disc was spun at 3000 rpm for 1 minute. The columns were rinsedwith water containing 0.1% TFA (trifluoroacetic acid, Aldrich)) twotimes. The rinsing was performed at an rpm of 2500 for ca 1 minute. 200nL of in-solution tryptic digest of BSA was added to individual channelsthrough the sample inlet. The following procedure was used fordigestion. The BSA (Sigma) was dissolved to a final concentration of4.75 pmol/μl in 0.1 ammoniumbicarbonate buffer at pH8. Theenzyme-modified trypsin (Promega Corp., Madison, Wis.) was added anddissolved at a ratio of BSA/trypsin 20:1. The sample was incubated at37° for 4 hours and then stored at −20° C. until used.

The sample was allowed to pass over the reversed phase columns at 1500rpm. A second rinsing/washing step was performed as above using watercontaining 0.1% TFA. Finally the peptides were eluted using 200 nLeluent consisting 50% isopropanol, 50% water andα-cyano-4-hydroxycinnamic acid (Aldrich) below saturation. The eluentwas prepared by saturating a water:isopropanol (50%) mixture withα-cyano-4-hydroxycinnamic acid. To 100 μL of this mixture 200 μL of 50%water:50% isopropanol was added, resulting in an eluent saturated toapproximately ⅔ with α-cyano-4-hydroxycinnamic acid.

The presentation of the sample in the MALDI port was performed in twodifferent ways.

-   -   a) In the first example a full structure was utilised (FIG. 2).        Eluent from the column was collected in the container placed at        an outer radial position relative of the reversed phase column.        When the lid was removed the liquid quickly evaporated leaving        co-crystallized matrix and peptides on the gold sputtered        surface. The disc was cut in halves to fit in the MALDI        ionisation interface.    -   b) The moulded structure was cut directly after the packed        column leaving an open-ended microstucture. The eluent was        allowed to pass the column at a pre-determined speed (1500 rpm)        in order to generate a controlled evaporation of the solvent at        the MALDI port, and hence the formation of co-crystallized        matrix and peptides suitable for MALDI analysis. The disc was        cut in halves to fit in the MALDI ionisation interface.

EXAMPLE 4

Structured CD and Site-specific Elution

This example employs a CD with integrated microfluidic structures, athin (≦70 μm) lid with holes at positions matching the MALDI port in theCD. The microfluidic structure employed in this example is shown in FIG.1.

The polycarbonate CD was covered with gold as described above. The sidewas hydrophilized using the thiolprocedure described above. The lid(SkultunaFlexible, Skultuna, Sweden), having, pre-drilled holes, wasattached to the CD through heat pressing at 135° C.

Reversed phase beads (Source 15 RPC) with a diameter of 15 μm werepacked in the individual structures using capillary forces incombination with centrifugation. The columns were rinsed with ethanoland spun to dryness before 23 fmol of tryptically digested BSA was addedand spun down using 700 rpm. The tryptic digest of BSA was generatedaccording to the procedure described above. After sample addition, thecolumn was rinsed twice with water. α-cyano-4-hydroxycinnamic acid wasmixed in an organic solvent of acetonitril/water 3:7 containing 0.1% TFAto a saturation of ⅔ and 250 nl was used to elute the sample from the 3nl packed column.

The crystals obtained after evaporation of the organic/water mixturecontained co-crystallized peptides. Eight singly charged peptide peakswere present in the mass spectrum obtained

1. A method for presenting an analyte of a liquid sample as anMS-analyte to a mass spectrometer comprising the steps of: (i) applyingthe liquid sample containing the analyte to a sample inlet port of amicrochannel structure of a microfluidic device, said microchannelstructure comprises an outlet port (MS-port) that is interfaced with amass spectrometer and inertia force is used for liquid transportationwithin at least a part of said microchannel structure; (ii) passing theanalyte to the MS-port thereby transforming the analyte to anMS-analyte, and (iii) presenting the MS-analyte to the mass spectrometervia the MS-port.
 2. The method of claim 1, wherein the analyte is abiopolymer comprising a carbohydrate structure, a nucleic acid structureor a peptide structure.
 3. The method of claim 1, wherein the analytecomprises a peptide structure.
 4. The method of claim 1, whereintransformation of said analyte to an MS-analyte comprises digestion ofthe analyte into fragments.
 5. The method of claim 4, wherein saiddigestion is a chemical digestion or an enzymatic digestion.
 6. Themethod of claim 1, wherein transformation of said analyte to anMS-analyte comprises chemical derivatization of the analyte.
 7. Themethod of claim 1, wherein transformation of said analyte to anMS-analyte comprises mass tagging of said analyte or of a derivativeformed during the transformation.
 8. The method of to claim 7, whereinsaid derivative to be mass tagged is a fragment of the analyte.
 9. Themethod of claim 1, wherein the inertia force is centrifugal force. 10.The method of claim 1, wherein said MS-port comprises an openingpermitting release of the MS-analytes into the mass spectrometer. 11.The method of claim 1, wherein said microfluidic device comprises aplanar substrate having at least one microchannel structure that extendsradially in the plane of the substrate with said MS-pen being located atan outer position and said sample inlet port at an inner position. 12.The method of claim 11, wherein said planar substrate alter orsimultaneously with the application of the sample is spun around itscentral axis which is perpendicular to said plane thereby forcingliquids present in the microchannel structure to move outwards.
 13. Themethod of claim 11 wherein said microfluidic device comprises aplurality of said microchannel structures.
 14. The method of claim 11,wherein the plurality of microchannel structures are annularly arrangedaround a central axis.
 15. The method of claim 14, wherein each EDI areacomprises a conducting layer (layer I) with a conductive connection. 16.The method of claim 15, wherein said separation zone comprises aseparation medium which is capable of selectively capturing saidderivative when a liquid containing said derivative is allowed to passthrough the zone.
 17. The method of claim 15, wherein transformation ofan analyte to said MS-analyte occurs in a reaction zone in saidmicrochannel.
 18. The method of 15, wherein said separation zoneseparates, concentrates, or purifies the analyte, MS-analyte orderivative thereof.
 19. The method of claim 15, wherein said separationzone comprises separation medium which exhibits ligand structures thatare capable of binding to said analyte or said MS-analyte or derivativeby affinity or reversible covalent bonds.
 20. The method of claim 15,wherein the separation zone is located downstream the sample inlet portand upstream the MS port.
 21. The method of claim 15, wherein theseparation zone is located within the MS-port.
 22. The method of claim1, wherein the MS-port comprises an electro spray arrangement.
 23. Themethod of claim 22, wherein there are two or more EDI areas on themicrofluidic device and that layer I in at least two of said EDI areasare present in a common continuous conducting layer comprising theconnection for electricity.
 24. The method of claim 1, wherein theMS-port comprises an EDI arrangement with an EDI area.
 25. The method ofclaim 1, wherein the microchannel structure further comprises aseparation zone.
 26. The method of claim 25, wherein said separationzone and said reaction zone coincide.
 27. The method of claim 1, whereinthe MS-analyte is a derivative of the analyte.